Fiber optic cross-connects and patch-panels are used to terminate large numbers of optical fibers at an array of connectors, providing a central location to manually or semi-manually interconnect network devices with patchcords. Typical cross-connect systems interconnect 100 to 10,000 network devices with complete flexibility. Connections between various types of transmission equipment, such as transceivers, amplifiers, switches and to outside plant cables destined for other exchanges, local offices, central offices, optical line terminations and points-of-presence are configured by manually installing jumpers to create communication links between specified pairs of ports.
For FTTH (Fiber-to-the-Home) and access networks, for example, the deployment of cross-connects are geographically dispersed and the number of ports is increasing significantly. Consequently, the tasks of allocating, reconfiguring and testing a fiber circuit within the network is challenging. There is significant potential for errors or damage resulting from manual changes to the physical network configuration. There is a need to automate the highly manual process of managing physical interconnections.
Robotically reconfigurable cross-connects can reduce the operational and maintenance costs of the network, improve the delivery of new services to customers and leverage costly test and diagnostic equipment by switching or sharing it across the entire network. It is appealing from a cost, accuracy and response-time perspective to configure the cross-connect from a remote network management center through network management software. The key building block of an automated patch-panel system is a scalable, high port count, all-optical cross-connect switch.
Typical networks are now installed in an incremental fashion so that fiber circuits are added to the system as needed. Prior art automated cross-connect approaches have not been modular and as such, they do not offer an upgrade path from 200 ports to 1000 ports, for example. To achieve port counts above several hundred using existing technologies, a three-stage Clos network interconnection scheme must be implemented [C. Clos, “A study of non-blocking switching networks” Bell System Technical Journal 32 (5) pp. 406-424 (1953)]. This approach increases cost, complexity and reduces optical performance because of the need to transmit through a series arrangement of three switches rather than one.
The optical performance of prior art robotic cross-connects is inferior to manual patch-panels because they introduce an additional fiber optic connection in series with each fiber circuit. A manual patch-panel requires only one connector per circuit and offers a typical loss of <0.25 dB, while the equivalent robotic patch-panel incorporates at least two connectors per circuit. This increases the loss by at least a factor of 2 above manual systems.
A series of patents by Lucent, NTT and Sumitomo disclose various implementations of large port count optical cross-connects in which fiber optic connections are reconfigured by a robotic fiber handler. For example, Goossen describes a switch utilizing a circular fiber bundle and a circular ferrule loader ring in U.S. Pat. No. 6,307,983. U.S. Pat. No. 5,613,021, entitled “Optical Fiber Switching Device Having One Of A Robot Mechanism And An Optical Fiber Length Adjustment Unit” to Saito et al., describes the use of a robotic fiber handler to mechanically reconfigure connectors on a coupling board. U.S. Pat. No. 5,784,515, entitled “Optical Fiber Cross Connection Apparatus and Method” to Tamaru et al. describes a switch in which connectorized optical fibers are exchanged between an “arrangement board” and a “connection board” by a mechanized fiber handler. A motorized means of fiber payout is further described. Related approaches are described in a series of patents including JP7333530, JP11142674, JP11142674, JP10051815 and JP7104201.
To overcome the prior art's susceptibility to fiber entanglement, Sjolinder described an approach to independently translate fiber connectors along separate, linear paths in two spaced-apart planes on opposite sides of an honeycomb interface plate [“Mechanical Optical Fibre Cross Connect” (Proc. Photon. Switching, PFA4, Salt Lake City, Utah, March 1995]. In the first active switch plane, N linearly translating connectors are driven along spaced-apart rows by actuators and in the second active switch plane, an additional N linearly translating connectors are driven along spaced-apart columns. Row and column actuators are configured perpendicular to one another. Connections are made between fiber pairs located in any row and in any column by mating connectors at any of the N2 common insertion points within the interface plate. This approach requires at least 2N actuators to arbitrarily connect N inputs with N outputs. An extension of this cross-connect approach is disclosed in U.S. Pat. No. 6,859,575 by Arol et al., U.S. Pat. No. 6,961,486 by Lemoff et al. and WO2006054279A1 by J. Arol et al.
Robotic cross-connect approaches have the potential to perform substantially better from the standpoint of optical performance and maintain signal transmission even in the absence of electrical power. However, the scalability of these prior art robotic versions has been limited. The footprint of these versions scales as N2, where N is the number of circuits. Considering that the central offices of today's telecommunications service providers already utilize 1000 to 10,000 port patch panels, scalability is of prime importance. Therefore, an approach scaling linearly in N would enable the cross-connect to achieve a substantially higher port density commensurate with manual patch-panels. Automated fiber optic patch panels demand scalability to port counts in excess of 1000 within the footprint of a manual patch panel, modularity and the ability to incrementally add circuits on an as-needed basis. Current technologies have been unable to achieve these varied requirements.
A new concept for fiber optic switching which achieves these requirements is based upon extensions of the Theory of Knots and Braids and the mathematics of topology to fiber optic matrix switches. This approach is described in A. Kewitsch, Journal of Lightwave Technology, August 2009, as well as the two patent applications referenced above. The unique cross-connect architectures and reconfiguration algorithms resulting from new mathematical concepts disclosed herein overcome the scalability and optical performance limitations of the prior art.